In Swiss Pat. No. 462,392, a process is disclosed for dosing two varieties of molding sand into a molding box of a foundry mold using two sand hoppers or silos with assigned delivery mechanisms and an intermediate container disposed below the silos, the bottom of the intermediate container being formed by a louver closure. The molding box is filled by opening the louver closure of the intermediate container after the container has been placed over the molding box.
This process has the disadvantage that the molding sand is poured into the molding box practically uncompacted and, therefore, when a high quality mold is to be produced, it is necessary to employ two compacting operations, for example, a first operation involving shaking and a subsequent operation by pressing, or using vibration pressing.
From the Journal "Litjnoe Proizvodstvo in Deutsch," issue of 1962, pages 38 and 39, an experiment for compact molding by gravity and pressing is known. A mold having lateral dimensions of 600.times.700 millimeters and 250 millimeters in height was filled with a sand filling of 500 millimeters height from a doser the bottom of which is closed by a slide. The slide of the doser was opened quickly for the filling. The experiment resulted in the strongest compaction in the lower layers of the sand filling and no compaction in the upper layers. In the further course of the experiment, a smaller compaction was found to exist along the walls of the molding box and dropped even more in the corners of the molding box. No experiments with larger molds have been known. Such experiments would have shown even worse results because of the longer time needed for opening the doser slides. These results show that the process employed in the experiment is not suitable to avoid the known insufficiencies occurring during compacting of a sand mold by a precompacting taking place during filling.